1. Field of the Invention
The invention is generally directed to degradative enzymes and systems. In particular, the present invention is directed to plant cell wall degrading enzymes and associated proteins found in Microbulbifer degradans and systems containing such enzymes and/or proteins.
2. Background of the Invention
Cellulases and related enzymes have been utilized in food, beer, wine, animal feeds, textile production and laundering, pulp and paper industry, and agricultural industries. Various such uses are described in the paper “Cellulases and related enzymes in biotechnology” by M. K. Bhat (Biotechnical Advances 18 (2000) 355383), the subject matter of which is hereby incorporated by reference in its entirety.
Saccharophagus degradans strain 2-40 (herein referred to as “S. degradans 2-40” or “2-40”) is a representative of an emerging group of marine bacteria that degrade complex polysaccharides (CP). S. degradans has been deposited at the American Type Culture Collection and bears accession number ATCC 43961. S. degradans 2-40, formerly known and referred to synonomously herein as Microbulbifer degradans strain 2-40 (“M. degradans 2-40”), is a marine y-proteobacterium that was isolated from decaying Sparina altemiflora, a salt marsh cord grass in the Chesapeake Bay watershed. Consistent with its isolation from decaying plant matter, S. degradans strain 2-40 is able to degrade many complex polysaccharides, including cellulose, pectin, xylan, and chitin, which are common components of the cell walls of higher plants. S. degradans strain 2-40 is also able to depolymerize algal cell wall components, such as agar, agarose, and laminarin, as well as protein, starch, pullulan, and alginic acid. In addition to degrading this plethora of polymers, S. degradans strain 2-40 can utilize each of the polysaccharides as the sole carbon source. Therefore, S. degradans strain 2-40 is not only an excellent model of microbial degradation of insoluble complex polysaccharides (ICPs) but can also be used as a paradigm for complete metabolism of these ICPs. ICPs are polymerized saccharides that are used for form and structure in animals and plants. They are insoluble in water and therefore are difficult to break down.
Microbulbifer degradans strain 2-40 requires at least 1% sea salts for growth and will tolerate salt concentrations as high as 10%. It is a highly pleomorphic, Gram-negative bacterium that is aerobic, generally rod-shaped, and motile by means of a single polar flagellum. Previous work has determined that 2-40 can degrade at least 10 different carbohydrate polymers (CP), including agar, chitin, alginic acid, carboxymethylcellulose (CMC), 6-glucan, laminarin, pectin, pullulan, starch and xylan (Ensor, Stotz et al. 1999). In addition, it has been shown to synthesize a true tyrosinase (Kelley, Coyne et al. 1990). 16S rDNA analysis shows that 2-40 is a member of the gamma-subclass of the phylum Proteobacteria, related to Microbulbifer hydrolyticus (Gonzalez and Weiner 2000) and to Teridinibacter sp., (Distel, Morrill et al. 2002) cellulolytic nitrogen-fixing bacteria that are symbionts of shipworms.
The agarase, chitinase and alginase systems have been generally characterized. Zymogram activity gels indicate that all three systems are comprised of multiple depolymerases and multiple lines of evidence suggest that at least some of these depolymerases are attached to the cell surface (Stotz 1994; Whitehead 1997; Chakravorty 1998). Activity assays reveal that the majority of 2-40 enzyme activity resides with the cell fraction during logarithmic growth on CP, while in later growth phases the bulk of the activity is found in the supernatant and cell-bound activity decreases dramatically (Stotz 1994). Growth on CP is also accompanied by dramatic alterations in cell morphology. Glucose-grown cultures of 2-40 are relatively uniform in cell size and shape, with generally smooth and featureless cell surfaces. However, when grown on agarose, alginate, or chitin, 2-40 cells exhibit novel surface structures and features.
These exo- and extra-cellular structures (ES) include small protuberances, ger bleb-like structures that appear to be released from the cell, fine fimbrae or pili, and a network of fibril-like appendages which may be tubules of some kind. Immunoelectron microscopy has shown that agarases, alginases and/or chitinases are localized in at least some types of 2-40 ES. The surface topology and pattern of immunolocalization of 2-40 enzymes to surface protuberances are very similar to what is seen with cellulolytic members of the genus Clostridium. 
There exists a need to identify enzyme systems that use cellulose as a substrate, express the genes encoding the proteins using suitable vectors, identify and isolate the amino acid products (enzymes and non-enzymatic products), and use these products as well as organisms containing these genes for purposes such as those described in the Bhat paper.